The present invention relates to a developing device, a process cartridge and an image forming apparatus of which shape of a discharging wall forming a developer vent improved to discharge developer through the overflow while supplying toner and carrier to a developer container.
Out of dry type two-component developer comprising toner and carrier, toner is consumed by the image forming but carrier remains in the developing device. The resin material coated on the surface of the remained carrier is peeled off, toner component is adhered to the carrier surface and the charging efficiency and others as developer are lowered. And as a result of the lower of charging efficiency of developer, image quality can be deteriorated.
In view of the above, a system to supply carrier separately from the supply of toner that is consumed in the image forming is proposed. Here, toner is consumed by the image formation but carrier remains in a developer container of a developing device. Therefore, when it is tried to maintain the toner density at a constant level, volume of developer in the developer container increases. The developer that becomes excess in the developer container overflowed and discharged through the developer vent provided on the wall surface of the developer container.
When developer is supplied and discharged repeatedly as described above, deteriorated developer in the developer container is replaced with newly supplied developer, the characteristic of developer was maintained favorably and volume of developer was maintained at a constant level.
In such the developing device, as disclosed in the Japanese Patent Application Publication No. 7-121017, the volume of developer discharged by the overflow was affected by the shape of the developer vent to discharge developer and some of them were formed in the characteristic shape.
The volume of developer discharged by the overflow is influenced by the shape of the developer vent and also by the sectional shape of the developer vent. For example, developer is discharged through the developer vent and at this time, developer is deposited on the tip part of the discharge dam forming the developer vent. As a result, the height of the discharge dam becomes substantially high and the area of the developer vent decreases. Thus, the developer discharging volume decreases and the volume of developer in the developer container increases.